This invention relates to a composite material having corrosion resistance in extremely corrosive environments and a method of manufacture typically for use in heat exchanger applications.
It has been known to manufacture plate-and-fin type stainless steel heat exchangers by brazing the plates of the unit with copper. The brazing prevents leakage from the channels by sealing each plate around the edge and at the ports. In such a design no gaskets or frames need be used which results in a compact, cost effective design. These brazed units further have thermal efficiency advantages over the gasketed plate heat exchangers. Such a brazed unit can be constructed from "self-brazing" composite material such as copper bonded to the stainless steel or nickel super alloy plate material. Such self-braze composite materials provide for reliable and economical manufacture of the heat exchanger units.
Deficiencies in the above described unit occur, however, in applications in which high temperatures are experienced or in which a corrosive material to copper is used as the heat exchanger fluid such as ammonia and acidic solutions. In such applications the copper braze material is unacceptable and a replacement is needed. One proposed replacement is a class of nickel base materials with alloying additions such as silicon and boron to reduce the melting point. These materials, however, are quite brittle and thereby only allow for fabrication as a preform foil in an amorphous state by rapidly quenching or as a preform of powder in a binder. These preforms cannot be readily formed or bonded to the plate material to form a self-brazing composite and therefore require extra handling and precise positioning when fabricating the heat exchanger. These extra handling steps can also effect the reliability of the braze; and ultimately, the final product.